Liquid development apparatus for development of electrostatic images

ABSTRACT

An inclined fine mesh screen of conductive material, in combination with a reservoir or liquid medium having toner therein, supports a body bearing an electrostatic latent image to be developed. Means dispense the toner charged liquid across the upper portion of the inclined screen.

United States Patent [72] Inventors Guy A. Marlor;

John A. Dahlquist, Palo Alto; Eugene F.

Cirimele, Sunnyvale, Calif. [21 Appl. No. 798,304 [22] Filed Feb. 1 1, 1969 [45] Patented Mar. 16, 1971 [73] Assignee Varian Associates Palo Alto, Calif.

[54] LIQUID DEVELOPMENT APPARATUS FOR DEVELOPMENT OF ELECTROSTATIC IMAGES -4 Claims, S-Drawing Figs.

[52] US. Cl 118/637 [51] Int. Cl B051) 5/00 [50] Field of Search 118/637,

637 (LX), 620;117/17.5, 37 (LX); 95/(Inquired); 355/(Inquired); 346/(1nquired) [56] References Cited UNITED STATES PATENTS 1,741,486 12/1929 Tibbetts et a1. 1 18/243 3,001,888 9/1961 Metcalfe et a1.. 117/37(LX) 7 3,079,890 3/1963 Oliphant 117/37X(LX) 3,165,047 1/1965 l-lersh ...(l18/637(LX)) 3,202,092 8/1965 Childress l18/637X 3,220,833 11/1965 McFarlane 117/17.5X 3,245,341 4/1966 Childress et a1. 117/17.5X 3,356,066 12/1967 Larsson et a1 118/401X 3,415,223 12/1968 Zweig 118/637 3,504,624 4/1970 Kennedy, Jr 113/637X OTHER REFERENCES IBM Technical Disclosure Bulletin, Drying Rate Monitor For Liquid Developer Copy Machines Lahr, R. J. (April 1965) Vol. 7 No. 11 pg. 981- 982, copy 1 l8/637LX IBM Technical Disclosure Bulletin, Developing Electrostatic Charge Patterns Crawford, T.M., (Sept. 1965) Vol. 8

- No.4, Pg. 527, Copy 118/637LX Primary ExaminerMorris-Kaplan Attorneys-William J. Nolan and Leon F. Herbert ABSTRACT: An inclined fine mesh screen of conductive material," in combination with a reservoir or liquid medium having toner therein, supports a body bearing an electrostatic latent image to be developed. Means dispense the toner charged liquid across the upper portion of the inclined screen.

Patented March 16, 1971 2 Sheets-Sheet 1 INVENTORS GUY A. MARLOR JOHN RDAHLQUIST I EUGENE CIRIMELE 'BY W n/726W ATTORNEYS Patented March 16, 1971 3,570,456

2 Sheets-Sheet 2 FIG.4 Q 40 s I I U m 50 INVENTORS GUY A. MARLOR JOHN A. DAHLOUIST EUGENE E CIRIMELE ll wmflliwlw ATTORNEY room DEVELOPMENT APPTUS FOR DEVELOPMENT OF ELECTROSTATIC IMAGES DESCRIPTION OF THE PRIOR ART The present invention relates in general to the development of electrostatic images created on dielectric mediums, and in particular, to a liquid toner development system for use in electrostatic and electrophotographic cameras and copiers.

lln electrostatic and electrophotographic recording, electrostatic images are created or formed by laying down a charge in predetermined patterns on a dielectric medium by means of either conductive stylii or photoconductive plates. The charged medium is then developed, that is, the charge patterns are made visible by the application of either a dry or liquid toner which comprises opaque oppositely charged particles, such as carbon. The toner particles are attracted to the dielectric medium by the charge patterns and then fixed by heat, evaporation of a solvent or by another appropriate method.

In practice, the application of liquid toner to the charged surfaces of dielectric mediums has been achieved in a variety of ways by a variety of apparatus including: slotted inking channels as in the manner of Lloyd, U.S. Pat. No. 3,392,706; spraying and immersion of the medium in the toner as in the manner of Hastings et al., U.S. Pat. No. 3,359,945; and webbing or belts with raised patterns comprising fine lines'or dots as in the manner of Gundlack, US. Pat. No. 3,084,043.

While each of the described apparatus may in general provide satisfactory prints, problems including excessive wetting of the paper and the absence of a suitable-backup electrode needed in low charge density applications have been encountered with slotted inkers, dirtying and background graying of the nonimage sides and image portions of the medium have been experienced with total immersiontechniques and insufficiency of supply of toner material would be expected with the raised belt technique especially if it was used in low charge density electrophotography applications.

SUMMARY OF THE INVENTION The present invention, described in more detail herein below, has been found to fill the need, particularly in electrophotography, for high speed development of high contrast prints without undesirable wetting and background graying of the nonimage sides and areas of a dielectric medium upon which electrostatic images are laid. To avoid graying under high density toners, conventional toners typically of from onehalf to 1 percent concentration or grams/cc. of colloidal carbon particles are used under high throughput conditions.

In accordance with the present invention, a fine mesh screen of conductive material has been found to provide a novel, simple and expeditious means and method for supplying and transporting more conventional relatively low density fresh toner to the image bearing surface of a dielectric medium in the development of the electrostatic images formed thereon than has been heretofore'possible. This is accomplished without excessive wetting of either the image bearing surface or the reverse side of the medium and more importantly, without any increase in medium to backup electrode distance.

In one embodiment, the screen is formed into the shape of a cylinder and a portion caused to rotate in a reservoir of conventional iiquid toner, such as Hunt 27-10 made by the Philip Hunt Co., Palisades Park, NJ. The toner is picked up by the screen through capillary action or the effects of surface tension and carried to the point of contact between the cylinder and the dielectric medium. In the preferred embodiment the dielectric medium is dielectric coated conductive paper. The electrostatic image on the dielectric coated paper then withdraws out of the liquid toner by electrostatic attraction opaque toner particles with only a minimum contact, if any, between the paper and liquid itself though intimate contact with the conductive screen is maintained. By this means, excess toner whether picked up in the method just described or by the use of additional means of distribution within the cylinder will run off in the interior surface of the cylinder and thereby prevent excessive wetting of the paper. It may also be in certain instances preferable to rotate the cylinder against the direction of motion of the paper to increase the amount of toner supplied.

For the same reasons and for providing even a grater greater supply of toner particles to the image bearing surface, the present invention may be embodied in a planar mesh screen held taut by a rigid frame at an incline to the horizontal. The lower end of the inclinedscreen is placed in a reservoir of liquid toner. An apertured tubular liquid distributor is mounted to the upper surface of the high end of the screen and is maintained in liquid communication with the toner in the reservoir. By suitable means the toner is pumped from the reservoir to the apertured tubular distributor. The toner flows onto and through the upper portions of the screen and down into the reservoir on the under surface of the screen opposite the image bearing surface of the dielectric coated paper. In this manner nearly an unlimited amount of fresh conventional relatively low density toner may be presented for the development of even the darkest images under extremely low charge density conditions without increasing the paper-to-backup electrode distance.

Accordingly a principal object of the present invention is novel high speed apparatus for the development of electrostatic images.

A principal feature of the present invention in accordance with the object is a mesh screen for carrying toner to the electrostatic image bearing surface of a dielectric medium.

Other objects, features, and advantages of the present invention will be apparent in the consideration of the detailed description herein below when read in connection with the accompanying drawing.

DESCRIPTION OF THE DRAWING FIG. 1 is an isometric view of one embodiment of the present invention.

FIG. 2 is an isometric view of another embodiment of the present invention.

FIG. 3 is an isometric view of the cylinder of FIG. 2.

FIG. 4 is a side elevational view taken along the lines 4-4 of FIG. 2

FIG. 5 is a cross-sectional view taken along lines 55 of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, there is shown one embodiment of the present invention which may be used in the development of electrostatic images in a hand or manual mode or in combination with an automated paper transport system. While suitable for use in developing electrostatic images formed or created by any method on any type of suitable medium, apparatus made in accordance with the present invention is believed to have its greatest utility in the development of electrophotographically produced images on dielectric coated conductive paper. The reason for this is founded on the low charge density of images obtained by means of electrophotography and the consequent need for the full development of said image without development of the background. As is well known, a backup electrode in the development process of electrophotographically produced images is required to change the electric field pattern of the latent image and enhance the field. Other methods which would permit higher toner flow, however, are found to do so at the expense of the backup electrode, that is, by increased spacing between the electrode and the image bearing medium.

Accordingly, there is provided as shown in FIG. 1, a fine mesh screen 1 comprised of conductive materiai, such as copper or stainless steel. Screen 1, typically 40 to 60 mesh/in. and preferably 50 mesh/in, is held taut by a rigid frame 2 at an incline to the horizontal by a support 3. The lower end of screen 1 is maintained in a reservoir 4 which, in operation, is filled to a suitable level with a desired conventional liquid toner 14, as for example Hunt 27-l0 made by the Philip Hunt Co., Palisades Park, NJ. A suitable toner for use in developing electrostatic images of one charge comprises oppositely charged particles, such as carbon, held in colloidal suspension in a liquid base or solvent. The concentration of the toner is typically one-half to 1 percent or grams/cc. of colloidal carbon particles. The restriction on toner density is to prevent background graying and in turn, requires increased toner flow for complete development, that is, complete neutralization of the image charge within the shortest possible time. At the upper end of screen 1 there is provided an apertured tube M) for flooding screen i with toner 14. A pump ill in liquid communication with the toner 14 in the reservoir 4 circulates toner 14 from the reservoir 4 through hoses l2, 13 to apertured tube 10. The minimum number and size of the apertures and pump pressure are determined such that the upper portion of screen 1 is maintained fully flooded with toner M.

In operation with screen 1 maintained at the customary ground potential or some other suitable potential provided by a source, not shown, toner 14 is pumped throughout the length of apertured tube 10 and floods the upper portion of screen 1.

Within a short distance from apertured tube 10 practically all of toner l4 gravitates through screen 1 and migrates by means of capillary action and surface tension down the underside of screen 1 into reservoir 4. While it is understood that the upper surface of the screen is wetted by the toner liquid, the majority of the toner flows on the underside of the screen, thus allowing very intimate contact between the screen and the dielectric coated paper.

In the development process, a suitable electrostatic image bearing medium, as for example a dielectric coated conductive paper 54 as shown in FlG. 5, is placed face down on screen 1. The image of one charge attracts the oppositely charged particles from within toner M. It is now apparent and has been found that contact between the image bearing medium on the upper surface of screen 11 and the toner liquid 14 flowing on the under surface of screen 1 is at all times maintained at a minimum. That is to say, greatly increased amounts of toner 14 may be permitted to flood the underside of screen 1 without appreciably increasing the amount of liquid that comes in contact with the image bearingmedium.

Thus, in accordance with the present invention, the back surfaces of the image bearing medium remain dry eliminating the need for water or solvent proofing and the image bearing surface itself is found to be less subject to background graying with a resulting considerably increase in contrast between the image and nonimage areas. The image itself in spite of its low charge density is found also to be completely developed within a shorter period than heretofore possible.

ln FIGS. 2 and 3, there is shown an automated embodiment of the present invention in which the fine mesh screen 1 of FIG. l is shaped and held taut in the form of a cylinder by means of a rigid framework 21 comprising, for example, a pair of end plates 22 and one or more discs 23. Cylinder 20 is provided with a pair of axially disposed end shafts 24 and fitted freely into an assembly 25 comprising reservoir 4 as its base portion. At least one of said axially disposed end shafts 24 of cylinder 20 is adapted to receive a pulley or gear which is driven by means of a belt or chain 31 by a motor 32 mounted on the upper portion of assembly 25. A pair of input paper feed rollers 33 and a pair of output paper feed rollers 34 are held in place in assembly 25 by any suitable means, as for example, springs 35 on either side of cylinder 20. Preceding input rollers 33, there is further provided a roller 36 coupled to the lower one of rollers 33 by means of one or more belts 3'7. Roller 36 and belts 37 insure proper feeding of the image bearing paper between input feed rollers 33 from an input paper feed tray 38. Each pair of rollers 33, 34 are driven by a motor 40 mounted diagonally from motor 32 on the upper portion of assembl 25.

Referring to FIG 4, there is shown the driving assembly for rollers 33, 34. The lower one of each pair of rollers 33, 34 is fitted with a pulley or gear 41 and driven by means of belts or chains 42, 43 by motor 40. An idler pulley or gear 44 is provided intermediate pulleys 41 for taking up the slack in belt 42.

Referring to FIGS. 2 and 4, there is further provided in addition to the above-discussed rollers, three rollers 45 mounted in rolling relationship with the upper portion of cylinder 20 for insuring proper contract between the image bearing surface of a paper 50 and cylinder 20 as paper 50 passes therebetween.

In operation as paper 50 passes between rotating cylinder 20 and rollers 45, toner 14, previously picked up by means of capillary action or surface tension effects between toner M and fine mesh screen i, is brought in close contact with paper 50. Having been charged with an electrostatic image of one polarity by any suitable means as herein before discussed, paper 50 electrostatically withdraws opaque toner particles of opposite charge from toner 14. In the manner described with respect to the embodiment of FIG. 1, excess toner 14 which is bearing on the exterior surface of cylinder 20 will gravitate through screen 1 by the time the cylinder has rotated fresh toner to the point of development.

It is understood that various other arrangements can be made without departing from thescope of the present invention. For example, while shown rotating in a direction assisting the motion of the paper 50, cylinder 20 can be rotated in a direction opposing the motion of paper 50. In that event, the slight amount of toner which necessarily adheres to the exterior surface of cylinder 20 will act as alubricant overcoming deleterious effects of friction between paper 50 and cylinder 20. There may also be provided by means not shown, additional toner distribution means within the interior of cylinder 20, such as for example, an apertured tube 10 as shown in FIG. 1 for supplying fresh toner to cylinder 20 nearer the first point of development. Alternatively, a higher level of toner 14 can be maintained in reservoir 4.

It is also understood that other embodiments, such as endless belts, etc. could be used also.

I claim:

1. Developing apparatus for toning electrostatic images on a dielectric medium, the combination comprising:

a frame means;

a generally planar fine mesh screen of conductive material mounted on the frame means in an inclined position and adapted to transport liquid toner to the image bearing surface of the dielectric medium as the toner progresses down the inclined screen; and

a toner supply means adapted to supply the fine mesh screen with toner at the upper end thereof for replenishing the charged particles removed during the toning of the electrostatic images.

2. Developing apparatus according to claim 1 wherein the toner supply means comprises:

a reservoir in fluid communication with the lower end of the inclined screen for containing the toner after progressing down the inclined screen;

apertured tubular means disposed across the upper end of the inclined screen for providing a distribution of the toner across the surface of the inclined screen; and

means in liquid communication with the reservoir and the apertured tubular means for transporting toner from the reservoir to the apertured tubular means.

3. Developing apparatus according to claim 2 wherein the majority of toner distributed by said apertured tubular means to said incline screen floods and flows on the underside of said incline screen.

4. Developing apparatus according to claim 2 wherein said fine mesh screen is of a density of from 4D to 60 mesh/in. 

1. Developing apparatus for toning electrostatic images on a dielectric medium, the combination comprising: a frame means; a generally planar fine mesh screen of conductive material mounted on the frame means in an inclined position and adapted to transport liquid toner to the image bearing surface of the dielectric medium as the toner progresses down the inclined screen; and a toner supply means adapted to supply the fine mesh screen with toner at the upper end thereof for replenishing the charged particles removed during the toning of the electrostatic images.
 2. Developing apparatus according to claim 1 wherein the toner supply means comprises: a reservoir in fluid communication with the lower end of the inclined screen for containing the toner after progressing down the inclined screen; apertured tubular means disposed across the upper end of the inclined screen for providing a distribution of the toner across the surface of the inclined screen; and means in liquid communication with the reservoir and the apertured tubular means for transporting toner from the reservoir to the apertured tubular means.
 3. Developing apparatus according to claim 2 wherein the majority of toner distributed by said apertured tubular means to said incline screen floods and flows on the underside of said incline screen.
 4. Developing apparatus according to claim 2 wherein said fine mesh screen is of a density of from 40 to 60 mesh/in. 